Radio frequency (RF) power amplifiers are used to amplify an RF signal, such as for transmission over a wireless network. Some RF power amplifiers are switchable between a low-power mode and a high-power mode that provide different amplification gain. A switch is typically placed at the output of the low power mode to provide isolation during the high power mode and to pass the RF signal during the low power mode. However, the switch provides low isolation and a variable impedance at the third harmonic of the RF signal, which causes the RF power amplifier to have a low efficiency.